1. Field of the Invention
This invention relates to a catheter incorporating a microwave antenna that has an integrated structure and, more particularly, to a urethral balloon catheters having an integrated structure.
2. Description of the Prior Art
Urethra balloon catheters incorporating a microwave antenna for treating prostate disease are known in the art. In this regard, incorporated by reference herein is the teaching of U.S. Pat. No. 5,007,437, which issued Apr. 16, 1991 to Fred Sterzer and is assigned to the same assignee as the present application.
At the present time, microwave balloon treatment of Benign Prostate Hyperplasia (BPH) or prostate cancer involves the use of a urethral catheter with an inflatable balloon to stretch the opening in the enlarged prostate and a radiating antenna to apply microwave energy to the stretched prostatic urethra with the objective of forming a long-lasting biological stent to relieve the symptoms of the affliction. The use of a separate antenna or applicator which must be inserted into the catheter forces several design compromises on both the catheter and the antenna. For both elements to be completely independent and separable, the inserted member, the antenna, must be smaller in diameter than it should be for optimum radiation efficiency and minimum dissipative loss, and the catheter must be larger than needed and provide additional complex flow paths for inflation liquids and/or gasses.
When properly positioned for treatment, the antenna is located near the distal end of the catheter inside the enlarged prostate. It may be in the form of a helical radiator, a capacitive gap, or folded dipole, or other design consistent with the size restrictions (e.g., the length should be no longer than the prostate and the diameter must fit within the restrictive inner diameter of the central lumen of the catheter). For proper impedance match, compactness, and shielding, the connection or feed-line for this antenna must be a coaxial cable consisting of a metal central conducting wire and an outer thin-wall metal cylinder shield with a continuous dielectric insulation between the two metal members.
The catheter must be of a material that is sanitary, sterile, flexible, capable of being extruded with a number of small internal lumens, and tolerant of adhesives used to attach expansion and locating balloons of different physical properties. A number of modern day plastics, e.g. silicones, PET, Teflon.RTM., and Tefzel.RTM. are typically used because they are consistent with these requirements. Coincidentally, some of these very same plastics are used for the dielectric insulator in the coaxial feed-line and in some of the antennas.
Thus, the maximum size of the outer diameter of a urethral balloon catheter, with a deflated folded balloon, is limited to a size that will fit into the narrowed urethra of a male patient suffering from a prostate disease. The structure of a prior-art urethral balloon catheter incorporating a microwave antenna comprises separate first and second sub-structures. The first sub-structure consists of the longitudinal body of the prior-art catheter to which the catheter's balloon material is attached. The second part consists of a microwave antenna to which a coaxial cable is attached for supplying microwave power to the antenna. The longitudinal body of the first part includes a centrally-located lumen through which the microwave antenna and coaxial cable of the separate second part can be inserted. This necessitates that the centrally-located lumen diameter be enough larger than the consequent limited diameter of the coaxial cable and the width of the microwave antenna to provide sufficient clearance for their insertion into the centrally-located lumen. The amount of microwave power loss caused by this consequent limited diameter of the coaxial cable and the radiating inefficiency caused by this consequent limited width of the microwave antenna are both undesirable.
Therefore, there is a need for a urethral balloon catheter structure in which the microwave antenna with its attached coaxial cable are integrated with and, therefore, form a permanent part of the longitudinal body of the urethral balloon catheter, since this would permit a desirable increase in the diameter of the coaxial cable and width of the microwave antenna without any increase in the maximum size of the outer diameter of a urethral balloon catheter.